Wow, what a great idea from a multimedia team from Oberhausen/Germany:

“Tank-FX is a non-virtual effect device. The reverb is generated by
a huge 11m tank made of ferroconcrete. We put some mics and
speakers in it and connected them to a Unix box, so everybody can
use it now from the internet. To try it out, just upload some
audio material. It will be processed in real-time.”
Website

An additional very pleasant aspect of the project is that they only used free software, which is listed on the website.